Regulation of NAD+- and NADP+-linked isocitrate dehydrogenase in the obligate methylotrophic bacterium Pseudomonas W6
✍ Scribed by K. H. Hofmann; Dr. W. Babel
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 372 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0233-111X
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Cell‐free extracts of the obligate methanol‐utilizing bacterium Pseudomonas W6 catalyze the oxydation of isocitrate to α‐ketoglutarate in the presence of NAD^+^ and NADP^+^. After electro‐focusing of the crude extract of Pseudomonas W6 actually two distinct bands each of NAD^+^‐linked isocitrate dehydrogenase (NAD^+^‐IDH) and of NADP^+^‐linked isocitrate dehydrogenase (NADP^+^‐IDH) could be observed. The NAD^+^‐IDH was completely separated from the NADP^+^‐IDH by employing DEAE ion exchange chromatography and further purified by affinity chromatography using Cibacron blue F 3G‐A.
The NAD^+^‐IDH was inhibited by a high energy charge, whereas the NADP^+^‐IDH was found to be independent of energy charge. Consequently the NAD^+^‐IDH showed the control behaviour of an enzyme of an energy‐generating sequence which, however, equally fulfils a catabolic and an anabolic function. With respect to the inhibition by reduced pyridine nucleotides and α‐ketoglutarate differences between NAD^+^‐IDH and NADP^+^‐IDH were also found. Only the NADP^+^‐linked enzyme exhibited a feedback inhibition by its reaction products α‐ketoglutarate and NADPH. This control behaviour gives evidence for the biosynthetic function of the NADP^+^‐IDH. These results confer an amphibolic character to the sequence from citrate to α‐ketoglutarate in the incomplete citric‐acid cycle of Pseudomonas W6.